In vitro refolding of recombinant human free secretory component using equilibrium gradient dialysis

Expression, purification and functional identification of the modified hEGF protein

Human epidermal growth factor (hEGF) plays an important role in the growth and division of epithelial cells and has good application prospects in skin-related injuries and diseases. Weak skin penetration and rapid clearance of hEGF in skin via the mononuclear phagocyte system have restricted the application of hEGF. To overcome these shortcomings, the recombinant gene TAT-hEGF-CD47 was constructed in our experiments, and the fusion protein TAT-hEGF-CD47 was expressed, purified and renatured. The cell proliferation-promoting function, skin penetration and concentration of TAT-hEGF-CD47 in skin after its application were determined. The results showed that TAT-hEGF-CD47 effectively promoted human skin fibroblast and skin epithelial cell proliferation, and the proliferation-promoting effect was positively correlated with the TAT-hEGF-CD47 concentration. After administration to the skin, TAT-hEGF-CD47 effectively penetrated the epidermal layer of the skin because of the TAT domain and stayed in the skin for a long time because the CD47 fragment slowed its clearance via the mononuclear phagocytic system. In conclusion, TAT-hEGF-CD47 exhibits high cell proliferation-promoting activity, high skin penetration efficiency and long retention time in skin and has laid the foundation for its wide application in skin repair, ulcer, diabetes and even cancer treatments.

Comparison of polymeric immunoglobulin receptor between fish and mammals

Polymeric immunoglobulin receptor (pIgR) functions in transporting polymeric immunoglobulin across epithelial cells into external secretion in animals. During animal evolution, fish was situated at a transition point on the phylogenetic spectrum between species possessing only innate immunity (i.e., invertebrates) and species depending heavily on adaptive immunity (i.e., mammals). Previous studies reported that fish and mammals significantly differ in pIgR. This review summarized the differences in pIgR structure, function, and transcriptional regulation between fish and mammals. A model of the transcriptional regulation of the pIgR gene was suggested. In this model, microbes could activate Toll-like receptor, trigger the cascade reactions in the signaling pathway, and then activate transcription factors that regulate pIgR expression through combining with the pIgR promoter. This review provides some suggestions for further studies on the function and regulatory mechanism of pIgR in fish and other animals.

Molecular characterization of polymeric immunoglobulin receptor and expression response to Aeromonas hydrophila challenge in Carassius auratus

The polymeric immunoglobulin receptor (pIgR) plays a pivotal role in mucosal immune response by transporting polymeric immunoglobulins onto the surface of mucosal epithelia to protect animals from invading pathogens. In this study, the full-length cDNA of pIgR was firstly cloned in Qihe crucian carp (Carassius auratus), hereafter designated as CapIgR, by using reverse transcription polymerase chain reaction and rapid amplification of cDNA ends. The molecular characterization and expression of CapIgR were investigated. The full-length cDNA sequence of CapIgR was composed of 1409 bp, which included a 112 bp 5'-untranslated region (UTR), a 984 bp ORF, and a 313 bp 3'-UTR, with a putative polyadenylation signal sequence AATAAA located upstream of the poly(A) tail. The deduced amino acid sequence indicated that CapIgR was a single-spanning transmembrane protein with 327 amino acids and possessed a signal peptide, an extracellular region containing two immunoglobulin-like domains, a transmembrane region, and an intracellular region. The mRNA expression levels of CapIgR were detected in different tissues of healthy C. auratus by quantitative real-time PCR, and the highest expression level was found in the liver. After Aeromonas hydrophila challenge, CapIgR expression was upregulated in different tissues at certain time points, and temporal expression changes of CapIgR fluctuated in a time-dependent manner. CapIgR exhibited rapid immune response to A. hydrophila challenge and played an important role in the immune defense of fish. These findings provided insights into the structure, function, and immune defense mechanism of CapIgR in C. auratus. This study can serve as a basis for developing disease control strategies in aquaculture.

TAT-NEP1-40 as a novel therapeutic candidate for axonal regeneration and functional recovery after stroke

Currently available therapeutics has been less effective in promoting functional recovery from stroke or other injuries in the central nervous system (CNS). Axonal damage is a characteristic pathology seen in CNS injuries. Previously, it was reported that Nogo-A extracellular peptide residues 1-40 (NEP1-40), a competitive antagonist of Nogo-66 receptor (NgR1), has the ability to promote axonal regrowth and functional recovery after CNS injury. However, delivery of the therapeutic proteins into the brain parenchyma is limited due to its inability to cross the blood-brain barrier (BBB). We first generated a biologically active NEP1-40 fusion protein containing the protein transduction domain (PTD) of the transactivator of transcription (TAT), TAT-NEP1-40, which crosses the BBB in vivo after systemic delivery. The TAT-NEP1-40 can protect PC12 cells against oxygen and glucose deprivation (OGD) and promote neurite outgrowth when added exogenously to culture medium. The TAT-NEP1-40 protein transduced into the brain continued to sustain biological activities and protected the brain against ischemia/reperfusion injury through inhibition of neuronal apoptosis. Collectively, our data suggest that TAT-NEP1-40 may be a novel therapeutic candidate for axonal regeneration and functional recovery from CNS injuries such as cerebral hypoxia-ischemia, cerebral hemorrhage, brain trauma, and also for spinal cord injury.

Clinical research progress in secretory component structure and function

SIgA, which consists of 2 monomer IgA, 1 molecular chain J and a molecular secretory component (SC), plays a critical role and is considered as the first-line defense in the mucosal immunity. As an important part of SIgA, SC is the extracellular cleaved ectodomain of polymeric immunoglobulin receptor (pIgR). SC plays an important role in the formation and transportation of SIgA and SC could also protect the hinge area of SIgA and enhance its anti-infective activity. Therefore, the SC has attracted increasing attention from researchers and great progress has been recently made in its structure and function.

TAT-mediated protein transduction of Nogo extracellular peptide 1-40 and its biological activity

AIM

Nogo extracellular peptide 1-40 (NEP1-40), a Nogo-66 antagonistic peptide, is one of the potential candidates for therapeutic intervention after central nervous system injury. This study is focused on the generation of TAT-NEP1-40 fusion protein and its transducible effects and biological activity.

METHODS

TAT-NEP1-40 fusion protein was expressed in vitro. Transducible effects of TAT-NEP1-40 were analyzed by using immunofluorescence staining or Western blot in vitro and in vivo. The biological activity of TAT-NEP1-40 was assessed by its effects against oxygen and glucose deprivation (OGD)-induced PC12 cell damages.

RESULTS

Our results showed that the TAT-NEP1-40 fusion protein was successfully expressed, purified, and refolded. Western blot analysis and immunofluorescence staining confirmed the delivery of TAT-NEP1-40 protein into PC12 cells and rat brains. OGD caused cell apoptosis or death, decreased cell viability, increased lactate dehydrogenase release in medium and the Bax/Bcl-2 ratio, all of which were prevented by the TAT-NEP1-40 fusion proteins when added exogenously to culture medium. In addition, TAT-NEP1-40 promoted neurite outgrowth of PC12 cells exposed to OGD.

CONCLUSION

These results demonstrate that the TAT-NEP1-40 can be successfully generated and efficiently transduced into PC12 cells and rat brains. The TAT-NEP1-40 can protect PC12 cells against OGD and promote neurite outgrowth. This finding suggests that the transducible TAT-NEP1-40 fusion protein offers a possibility of the development of novel therapy for cerebral injuries via delivery of the biologically active TAT-NEP1-40 fusion protein into injured sites.

Oscillatory molecular driving force for protein folding at high concentration: a molecular simulation

This paper presents a Langevin dynamics simulation that suggests a novel way to fold protein at high concentration, a fundamental issue in neurodegenerative diseases in vivo and the production of recombinant proteins in vitro. The simulation indicates that the folding of a coarse-grained beta-barrel protein at high concentration follows the "collapse-rearrangement" mechanism but it yields products of various forms, including single proteins in the native, misfolded, and uncollapsed forms and protein aggregates. Misfolded and uncollapased proteins are the "nucleus" of the aggregates that also encapsulate some correctly folded proteins (native proteins). An optimum hydrophobic interaction strength (epsilon*(p)) between the hydrophobic beads of the model protein, which results from a compromise between the kinetics of collapse and rearrangement, is identified for use in increasing the rate of folding over aggregating. Increased protein concentration hinders the structural transitions in both collapse and rearrangement and thus favors aggregation. A new method for protein folding at high concentration is proposed, which uses an oscillatory molecular driving force (epsilon*(p)) to promote the dissociation of aggregates in the low epsilon*(p) regime while promoting folding at a high epsilon*(p). The advantage of this method in enhancing protein folding while depressing aggregation is illustrated by a comparison with the methods based on direct dilution or applying a denaturant gradient.